Check valve, manufacturing method thereof and container having check valve

ABSTRACT

In order to provide a check valve capable of sufficiently suppressing the mixing of air into the container even if a certain impact is applied to the container and also capable of stably maintaining good pouring of the content, a check valve  10  of the invention is formed of rubber material and manufactured by integral molding. The check valve  10  has a tubular main body  1  having openings  1   a  and  1   b  at opposite ends, a lid  3  arranged to close one opening  1   a  of the main body  1 , and a hinge  5  that connects the main body  1  and the lid  3 . The lid  3  has a projection  3   a  on the side surface  3   b , the projection  3   a  coming in contact with a peripheral edge of the opening  1   a  of the main body  1.

TECHNICAL FIELD

The present invention relates to a check valve, a manufacturing method thereof and a container having a check valve.

BACKGROUND ART

Some foods and beverages gradually deteriorate with time and one reason is oxidation due to contact with air. So-called vacuum containers are known as containers for inhibiting such oxidation of the content (see, for example, Patent Document 1).

In the container described in Patent Document 1, a check valve for preventing air from entering the container is attached to a pouring spout. The check valve has a structure having a slit formed in its domed head and the slit is configured to be opened when pressure is applied in the pouring direction of the content whereas it is closed when pressure is applied in the filling direction.

PRIOR ART REFERENCES Patent Documents

-   Patent Document 1: JP10-338239 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

When manufacturing a container having a pouring spout with a check valve incorporated in the spout, the size of the pouring spout of the container is designed depending on the kind, viscosity, etc., of the content and the size of the check valve to be incorporated in the pouring spout is determined accordingly. For example, when adopting a vacuum container for a tabletop soy sauce container and providing a check valve in the pouring spout of the container, the outer diameter of the check valve is limited to around 10-15 mm. In order to mass-produce such small-size check valves at low cost, integral molding using a mold is suitable.

The present inventors made various types of check valves and containers having such valves as trial products by way of integral molding and evaluated the trial products with regard to the occurrence of air mixing into the container and the pouring of the content. As a result, it was found that a lid 53 of a check valve 50 illustrated in FIGS. 8A and 8B got stuck in a tubular main body 51 when a certain impact was applied to the container and the lid 53 did not sufficiently serve as a valve (see Comparative Example 1). Note that a hinge 55 shown in FIGS. 8A and 8B is a portion connecting the main body 51 and the lid 53.

The invention has been made in order to solve the above-described problem and an object of the invention is to provide a check valve and a container having the same, whereby the mixing of air into the container can be sufficiently suppressed even if a certain impact is applied to the container and good pouring of the content can be stably maintained. Another object of the invention is to provide a method for manufacturing a check valve having the above advantageous effects in a manner sufficiently efficient at low cost.

Means for Solving the Problem

The check valve according to the invention is formed of rubber material and manufactured by integral molding. The check valve comprises: a tubular main body having openings at opposite ends; a lid arranged to close one opening of the main body; and a hinge that connects the main body and the lid and is adapted to open the one opening when force is applied to the lid outwardly from the main body side, and the lid has a projection on a side surface thereof, the projection coming in contact with a peripheral edge of the one opening of the main body.

The above check valve has the projection formed on the side surface of the lid and when the one opening of the main body is closed, the projection comes in contact with the peripheral edge of the one opening of the main body. Since such projection is formed, the lid does not easily get stuck in the opening of the main body even if a certain impact is applied to the check valve and the lid can stably serve as a valve.

Here, the projection formed on the side surface of the lid will be a so-called undercut portion in the molding process. When a molded body is manufactured through integral molding and if it includes an undercut portion, it cannot properly be taken out from the mold in the mold-releasing step because the undercut portion gets caught in the mold and the molded body could be broken in some cases. On the other hand, increasing the number of molds so as to avoid undercut portions would cause another problem of raising cost.

The check valve according to the invention can sufficiently avoid such problem arising from undercut without the use of any special mold. That is, since the check valve according to the invention is formed of rubber material having a predetermined hardness and elongation, the projection of the lid can properly be taken out from the mold even if the projection is an undercut portion. Accordingly, the manufacturing cost of the check valve can sufficiently be reduced. Note that the hardness of silicone rubber indicated herein is a value measured in accordance with JIS K6249 and the elongation indicated herein is a value measured in accordance with JIS K7127.

In the check valve according to the invention, from the viewpoint of simplifying the manufacturing process, it is preferable that the one opening of the main body be constituted by a linear portion which serves as the hinge and an arc-shaped portion. The term “arc” used herein means part of a circle or part of an ellipse.

In the check valve according to the invention, from the viewpoint of further ensuring that the lid is prevented from getting stuck in the through hole of the main body, it is preferable that the outer diameter R₁ of an arc-shaped portion of the lid be greater than the diameter R₂ of the arc-shaped portion of the opening and that the difference between R₁ and R₂ be from 0.06 mm to 0.50 mm. In the check valve according to the invention, it is further preferable that the side surface of the lid and the inner surface of the main body form an angle of 15-25 degrees. It is still further preferable that the rubber material have a hardness of 30-80 degrees and an elongation of 200-900%, since such rubber material allows check valves with sufficient mechanical strength to be obtained easily without causing problems due to undercut during the manufacturing process.

The container according to the invention comprises a container main body formed of a film and the above-described check valve attached to the container main body. Since the container has the above-described check valve, the mixing of air into the container can sufficiently be suppressed even if a certain impact is applied to the container. Consequently, deterioration of the content due to oxidation can sufficiently be suppressed. In addition, since good pouring of the content can be stably maintained by the effect of the above-described check valve, the container can be used for a substantially long period of time without any special handling by a user.

It is preferable that the container according to the invention further comprise a spout in which the check valve is mounted. In that case, it is also preferable that a liquid outlet at the tip of the spout be shaped to be narrowed in the middle and again broadened.

In the container according to the invention, it is further preferable that at least part of the main body of the check valve be formed to be thin enough to be able to deform according to a difference from atmospheric pressure when the check valve has a negative pressure inside and thereby allow the check valve to have a reduced volume. When the above-described container is returned to the upright position from the discharging position, the liquid which is going back to the lower part of the container causes negative pressure in the upper part of the container. When negative pressure is created as such, the main body of the check valve partly deforms to be dented according to the difference from atmospheric pressure. Due to the deformation of the check valve, negative pressure is created in the space between the check valve and the tip of the liquid outlet in the spout and, as a result, the liquid left at the tip of the liquid outlet is sucked back (returns to the container) by a volume corresponding to the deformed volume of the check valve. If the container is capped after such suck-back, no liquid adheres to the surrounding portion of the liquid outlet, resulting in the prevention of any dripping.

In the above-described container, it is preferable that the main body of the check valve have a stepped form composed of a small diameter part and a large diameter part and that the one opening be formed at the small diameter part.

In the above-described container, it is further preferable that the small diameter part be formed to be thinner than the large diameter part.

The invention provides a method for manufacturing the above-described check valve. That is, the invention provides a method for manufacturing a check valve which comprises: a tubular main body having openings at opposite ends; a lid arranged to close one opening of the main body; and a hinge that connects the main body and the lid and is adapted to open the one opening when force is applied to the lid outwardly from the main body side, the lid having a projection on a side surface thereof, the projection coming in contact with a peripheral edge of the one opening of the main body. The method comprises: a molding step of obtaining a molded body of rubber material having a hardness of 30-80 degrees and an elongation of 200-900% in a cavity having a concave portion to form the projection; a mold-releasing step of removing the molded body from the cavity; and a cutting step of separating the main body and the lid from each other except a portion serving as the hinge.

According to the above-described manufacturing method, since the hardness and elongation of the rubber material are 30-80 degrees and 200-900%, respectively, the portion to be formed into the projection of the lid can sufficiently be prevented from getting caught in the concave portion of the cavity and the molded body can smoothly be taken out of the mold. As a result, no special mold is needed and this attains sufficiently reduced manufacturing costs.

Effect of the Invention

By using the check valve according to the invention, the mixing of air into the container can be sufficiently suppressed even if a certain impact is applied to the container and good pouring of the content can be stably maintained. Further, by adopting the manufacturing method of a check valve according to the invention, a check valve having the above advantageous effects can be manufactured sufficiently efficiently at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment of the check valve according to the invention.

FIG. 2A is a top view and FIG. 2B is a cross-sectional view of the check valve shown in FIG. 1.

FIG. 3 is a cross-sectional view of the check valve shown in FIG. 1 when the lid thereof is opened.

FIG. 4 is a partial cross-sectional view of the check valve shown in FIG. 1 in which the vicinity of the lid is enlarged.

FIG. 5 is a perspective view of a flexible vacuum container comprising the check valve shown in FIG. 1.

FIG. 6A is a perspective view and FIG. 6B is a cross-sectional view of an outer body having the check valve shown in FIG. 1 incorporated therein.

FIG. 7 is a partial cross-sectional view illustrating another embodiment of the check valve according to the invention.

FIGS. 8A and 8B are cross-sectional views of a check valve according to comparative example 1.

FIG. 9 is a cross-sectional view of another embodiment of the invention including a check valve and an outer body (spout) having the check valve mounted therein.

FIG. 10 is a cross-sectional view of a check valve.

FIG. 11 is a cross sectional view of a check valve when the main body thereof is partly deformed.

FIG. 12 is a cross-sectional view of an outer body (spout) in which the liquid outlet thereof is enlarged.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the invention will be described in detail with reference to the attached drawings. In the descriptions below, the same or corresponding components are given the same reference numerals and any repetitive description will be omitted.

Check Valve

Referring to FIGS. 1-4, descriptions will be made regarding a check valve to be incorporated into a soy sauce container for household use, as an example. A check valve 10 according to the present embodiment is made of elastomer, such as rubber material, and manufactured, for example, by integral molding. As illustrated in FIGS. 1, 2A and 2B, the check valve 10 has: a tubular main body 1 having openings 1 a and 1 b at opposite ends thereof; a lid 3 arranged to close the opening 1 a at the tip of the main body 1; and a hinge 5 that connects the main body 1 and the lid 3. As is seen from FIG. 3, the hinge 5 functions as a hinge for the lid 3 and has flexibility to allow the opening 1 a of the main body 1 to be open when force F is applied to the lid 3 outwardly from the main body 1 side.

The main body 1 has a through hole 1 c longitudinally extending therethrough and the openings 1 a and 1 b are the opposite ends of the through hole 1 c. From the viewpoints of the pouring of soy sauce and usability, the through hole 1 c preferably has an inner diameter of about 5.0-7.0 mm. As shown in FIG. 1, the lower part of the main body 1 has a thick wall and the upper part has a thin wall. The outer diameters of the lower part (thick-wall portion) and the upper part (thin-wall portion) of the main body 1 are preferably about 12.8 mm and about 7.7-10.0 mm, respectively.

As shown in FIG. 1, the outer surface of the lower part of the main body 1 is partly formed as a planar surface 1 d and a projection 1 e is provided on the planar surface 1 d. The projection 1 e serves as a positioning mark used when fixing the check valve 10 to an outer body 32 (see FIGS. 6A and 6B).

The opening 1 a at the tip of the main body 1 is constituted by a linear portion L and an arc-shaped portion R, as shown in FIG. 1. The linear portion L of the opening 1 a is formed by a raised part if which is provided inside the through hole 1 c of the main body 1 in the vicinity of the opening 1 a. The hinge 5 is formed by making the linear portion L and a linear portion of the lid 3 as a continuous portion. Configuring the portion other than the portion constituting the hinge 5 in an arc shape can simplify the manufacturing process and is thus advantageous. That is, after integral molding, the lid 3 can be cut out of the main body 1 except the hinge 5 by a simple step of increasing the pressure inside the main body 1.

The lid 3 is connected to the main body 1 via the hinge 5 and arranged to close the opening 1 a of the main body 1. The lid 3 has a projection 3 a on the side surface 3 b thereof, the projection 3 a coming in contact with the peripheral edge of the opening 1 a of the main body 1. With this projection 3 a on the side surface 3 b of the lid 3, the lid 3 does not easily get stuck in the through hole 1 c of the main body 1 even if a certain impact is applied to the check valve 10 and the lid 3 can stably function as a valve. Here, in the lid 3, if the side close to the hinge 5 is called a base end and the opposite side is called a tip end, the projection 3 a is preferably provided at the tip end.

The projection 3 a preferably has a height (length from the side surface 3 b of the lid 3 to the tip of the projection 3 a) of 0.4-0.6 mm and more preferably 0.45-0.55 mm. When the height of the projection 3 a is less than 0.35 mm, the effect of preventing the lid 3 from getting stuck in the through hole 1 c cannot be sufficiently obtained. On the other hand, when the height exceeds 1.0 mm, problems due to undercut easily occur in the manufacturing process.

In order to further ensure that the lid 3 is prevented from getting stuck in the through hole 1 c of the main body 1, it is preferable that the outer diameter R₁ of an arc-shaped portion of the lid 3 be greater than the diameter R₂ of the arc-shaped portion R of the opening 1 a. The difference between R₁ and R₂ is preferably 0.06-0.50 mm and more preferably 0.08-0.25 mm. By making the difference greater than 0.06 mm, the lid does not easily get stuck in the through hole of the main body even if a certain impact is applied to the container due to a fall, etc., and, consequently, pouring is not obstructed. By making the difference less than 0.50 mm, the lid and the main body are not likely to be in a quasi-adhesion state, and, consequently, pouring is not obstructed. If the outer diameter of the lid is not uniform, for example, if the side surface of the lid 3 is tapered as shown in FIG. 2B, R₁ is regarded as representing the maximum outer diameter.

In order to form the hinge 5 and to efficiently cut out the main body 1 and the lid 3 from each other in the manufacturing process, the side surface 3 b of the lid 3 is preferably tapered such that the outer diameter decreases toward the main body 1 side from the top. The angle formed by the side surface 3 b of the lid 3 and the inner surface of the main body 1 (angle α in FIG. 4) is preferably 15-25 degrees. When the angle is greater than 15 degrees, the lid does not easily get stuck in the through hole of the main body and pouring is, consequently, not obstructed. When the angle is smaller than 25 degrees, functioning as a check valve can be further facilitated and the mixing of air does not easily occur.

Further, providing asperities on one or both of the contact portions of the main body 1 and the lid 3 of the check valve 10 is preferable. Such asperities can reduce the surface tension, resulting in preventing the main body 1 and the lid 3 from adhering to each other due to the surface tension of the content liquid and thereby allowing the valve to be easily opened. Examples of the way to provide asperities include adding a filler to the rubber material, more specifically, using a rubber material mixed with a filler for one or both of the main body 1 and the lid 3 of the check valve 10. Examples of such filler include pyrogenic silica fine powder, titanium oxide powder, alumina powder, ground quartz, ground cristobalite, diatomite powder, aluminosilicate powder, magnesium oxide powder, aluminium hydroxide powder, iron oxide powder, zinc oxide powder and heavy calcium carbonate powder. The content of the filler in the rubber material is preferably 1-50% by weight and more preferably 5-40% by weight. The average particle diameter of the filler is preferably 0.1-50 μm and more preferably 5-40 μm.

The check valve 10 is made of rubber material and manufactured through integral molding. Specific examples of the rubber material include silicone rubber and NBR. If the check valve is used for a food container, it is preferable to use silicone rubber for the rubber material.

The rubber material that constitutes the check valve 10 has a hardness of 30-80 degrees, preferably 40-70 degrees, and more preferably 50-60 degrees. The rubber material has an elongation of 200-900%, preferably 300-800%, and more preferably 400-700%. If the rubber material has a hardness of less than 30 degrees or an elongation of greater than 900%, the check valve 10 would not have sufficient mechanical strength. On the other hand, if the rubber material has a hardness of greater than 80 degrees or an elongation of less than 200%, problems due to undercut would occur in the manufacturing process.

Method for Manufacturing Check Valve

The method for manufacturing the check valve 10 includes (a) molding step, (b) cutting step and (c) cutting step.

(a) Molding Step

The molding step is to obtain a molded body of a rubber material having a hardness of 30-80 degrees and an elongation of 200-900% in a cavity having a concave portion to form the projection 3 a. When the raw material is cured within the cavity by applying heat or pressure, the process conditions are set so that the resulting molded body has a hardness and elongation within the above range.

(b) Mold-Releasing Step

The mold-releasing step is to remove the molded body from the cavity. The molded body is removed from the cavity, for example, by pulling the male and female molds in opposite directions along the longitudinal direction of the molded body. In the present embodiment, the portion to be formed into the projection 3 a of the check valve 10 is an undercut portion; however, since the rubber material that constitutes the molded body has a hardness and elongation within the above-described range, problems arising from the undercut portion can be sufficiently suppressed.

(c) Cutting Step

The cutting step is to cut the main body 1 and the lid 3 from each other, except the portion serving as the hinge 5. Since the opening 1 a of the main body 1 is constituted by the linear portion L and the arc-shaped portion R, when air is supplied into the molded body to increase the pressure inside the molded body, stress is concentrated to the arc-shaped portion R, which allows only the arc-shaped portion R to be cut out.

Flexible Vacuum Container with Check Valve

Referring next to FIGS. 5, 6A and 6B, descriptions will be made regarding a self-standing readily-transportable flexible vacuum container 30 having an outer body 32 in which a check valve 10 is incorporated. The container 30 comprises a container main body 31 formed of a transparent film having flexibility, an outer body 32 disposed diagonally at a shoulder of the container main body 31 and a check valve 10 incorporated in the outer body 32. The check valve 10 is incorporated in an orientation such that the lid 3 is located at the tip of the outer body 32 and that the hinge 5 extends horizontally and the projection 3 a is located below the hinge 5 when the container 30 stands with its bottom down (the state shown in FIG. 5).

Although the film constituting the container main body 31 may be a single layer film, a multilayer film is preferable. When the film is formed of multiple layers, the film is constituted by, for example, a base layer that serves as an outer layer when formed into a bag-like shape, a sealant layer that serves as an inner layer and an adhesive layer that bonds the base layer and the sealant layer to each other.

The outer body 32 is composed of a cap attachment part 32 a, a check valve fixing part 32 b provided below the cap attachment part 32 a and a joint 32 c provided further below the check valve fixing part 32 b. Note that no cap is shown in FIG. 5. The outer body 32 is attached to the container main body 31 by bonding the outer surface of the joint 32 c and the peripheral edge of the container main body 31 so that the cap attachment part 32 a and the check valve fixing part 32 b protrude out from the container main body 31. The outer body 32 may be one prepared by injection molding, etc. Examples of the material of the outer body 32 include synthetic resin such as polyethylene and polypropylene. Welding between the container main body 31 and the joint 32 c may be carried out by heat sealing, high-frequency sealing, hot air sealing, microwave heating, ultrasonic sealing and the like.

When the container 30 containing soy sauce therein is inclined, force is applied to the lid 3 of the check valve 10 in a direction from the inside to the outside thereof and the lid 3 is consequently opened outwardly, making the soy sauce pour out. When the container 30 is returned to the original orientation, negative pressure is created within the container 30 and force is applied to the lid 3 in a direction from the outside to the inside thereof. As a result, the opening 1 a of the check valve 10 is closed, preventing air from entering the container 30.

Since the container 30 has the check valve 10, the mixing of air into the container 30 can sufficiently be suppressed even if a certain impact is applied to the container 30. As a result, deterioration of soy sauce due to oxidation can be sufficiently suppressed. Further, good pouring of the content can stably be maintained due to the effect of the check valve 10 and the container 30 can thus be used for a considerably long period of time without any special handling of a user.

A preferred embodiment of the invention has been described in detail; however, the invention is not limited to the above-described embodiment. For example, while the projection 3 a is formed on part of the side surface 3 b of the lid 3 in the above-described embodiment, a configuration shown in FIG. 7 is possible in which the entire side surface 13 b of a lid 13 is tapered and the upper part thereof serves as a projection 13 a. In this configuration, the projection 13 a is an undercut portion; however, similarly to the above-described embodiment, problems due to the undercut portion can be sufficiently prevented by using a rubber material having a hardness and an elongation within the above-described range.

Further, the shape of the main body of the check valve is not limited to a cylindrical shape and the main body may have a tubular shape with an ellipse, rectangular or polygonal cross-section. Still further, the cross-section of the flow path of the through hole 1 c and the shape of the lid are not limited to an approximately circular shape and may be ellipse, rectangular or polygonal.

Furthermore, descriptions have been made in the above-described embodiment concerning a check value to be used for a soy sauce container, but the application of the check value and container according to the invention is not limited to such soy sauce containers. Containers provided with the check valve of the invention may be filled with other liquids, such as soft drinks, alcohol beverages, salad oil or liquid detergent.

Suck-Back Mechanism

As another embodiment of the invention, a container 30 having a suck-back mechanism will be described below (see FIGS. 9-12).

In the container 30 according to this embodiment, a liquid outlet 32 d formed at the tip of an outer body (hereinafter also referred to as a spout) 32 has a shape good for preventing liquid, such as soy sauce, from dripping when it is stopped pouring. For example, the liquid outlet 32 d is shaped to be narrowed in the middle and again broadened (see FIG. 9). However, when the container 30 is inclined to pour out a required amount of soy sauce and then returned to the upright position, some soy sauce remains at the liquid outlet 32 and such soy sauce could consequently cause dripping or contamination. In view of the above point, the container 30 according to the present embodiment is equipped with a suck-back mechanism.

Specifically, in the container 30, at least part of the main body 1 of the check valve 10 is formed to be thin enough to be able to deform according to the difference from atmospheric pressure when a negative pressure is created inside the check valve 10 and thereby allow the check valve 10 to have a reduced volume (see FIG. 10, etc.). Here, which portion is formed to be thin is not particularly limited; however, the check valve 10 used in the present embodiment is configured such that the main body 1 has a stepped form composed of a small diameter part 11 and a large diameter part 12 and the small diameter part 11 is formed of a thinner wall than that of the large diameter part 12 so as to have flexibility (see FIG. 11, etc.).

The operation of the suck-back mechanism in the above-described container 30 is as follows. First, when the container 30 is returned from the inclined discharging position to the upright (upstanding) position, the discharging of the soy sauce stops. Further, when the container is returned to the upright position, the lid 3 of the check valve 10 is by itself closed due to the elasticity of elastomer and the space from the lid 3 of the check valve 10 to the liquid outlet 32 d (represented by A in FIG. 9) and the space from the lid 3 of the check valve 10 toward the interior of the container 30 (represented by B in FIG. 9) are separated from each other within the spout 32. Here, if a cap (not shown in the drawings) is attached to the cap attachment part 32 a of the spout 32 with some soy sauce left at the tip of the liquid outlet 32 d (see FIG. 12), the left soy sauce will adhere to the surrounding portion of the liquid outlet 32 d, which would cause dripping.

In this respect, when the container 30 of the present embodiment is returned from the discharging position to the upright position, the soy sauce which is going back to the lower part of the container creates negative pressure in the upper part of the container 30 (represented by P in FIG. 1). When negative pressure is created as such, the main body 1 of the check valve 10 partly (in the present embodiment, the wall of the small diameter part 11) deforms to be dented according to the difference from atmospheric pressure (see FIG. 11). Due to the partial deformation of the check valve 10, negative pressure is created in space A of the spout 32 (the space between the lid 3 of the check valve 10 and the liquid outlet 32 d) and, as a result, the soy sauce left at the tip of the liquid outlet 32 d can be sucked back by a volume corresponding to the deformed volume of the check valve 10 (see FIG. 12). If a cap is attached after such suck-back, no soy sauce adheres to the surrounding portion of the liquid outlet 32 d, resulting in the prevention of any dripping. Note that the time taken for a user to attach a cap after the user has returned the container 30 from the discharging position to the upright position is expected to be 1-2 seconds if all goes smoothly, but this is enough time to suck back the soy sauce left at the liquid outlet 32 d in the container 30 according to the present embodiment.

EXAMPLES

The invention will be more specifically described below based on examples and comparative examples; however, the invention is not limited to the examples below.

Preparation of Molded Bodies of Examples 1-3

In order to prepare check valves having the configuration illustrated in FIG. 1 and having the dimensions shown in the respective columns of Examples 1-3 in Table 1, molded bodies were prepared in the following manner. That is, silicone rubber material was charged into a cavity constituted by two molds and subsequently cured within the cavity at 175° C. for six minutes, thereby obtaining a molded body. When the obtained molded body was removed out and its projection was observed under a microscope, no breakage was found. In each of Examples 1-3, the silicone rubber constituting the molded body had a hardness of 55 degrees and an elongation of 380%.

Preparation of Molded Bodies of Examples 4 and 5

In order to prepare check valves having the configuration illustrated in FIG. 1 and having the dimensions shown in the respective columns of Examples 4 and 5 in Table 2, molded bodies were prepared in the following manner. That is, silicone rubber material was charged into a cavity constituted by nine molds and subsequently cured within the cavity at 170° C. for 135 seconds, thereby obtaining a molded body. When the obtained molded body was removed out and its projection was observed under a microscope, no breakage was found. In each of Examples 4 and 5, the silicone rubber constituting the molded body had a hardness of 60 degrees and an elongation of 350%.

Preparation of Molded Body of Comparative Example 1

In order to prepare a check valve having the configuration illustrated in FIGS. 8A and 8B and having the dimensions shown in the column of Comparative Example 1 in Table 2, silicone rubber material was charged into a cavity constituted by one mold and the charged material was cured in the same manner as in Examples 1-3. As a result, a molded body having no projection in the lid was prepared. The silicone rubber constituting the molded body of Comparative Example 1 had a hardness of 55 degrees and an elongation of 380%.

Preparation of Check Valves of Examples 1-5 and Comparative Example 1

Check valves of Examples 1-5 and Comparative Example 1 were prepared by increasing the pressure inside the obtained molded bodies to cut out the portion other than the linear portion serving as a hinge in an arc-like form. In each of the check valves of Examples 1-5 and Comparative Example 1, the angle α between the side surface of the lid and the inner surface of the main body was set to 20 degrees.

Preparation of Flexible Vacuum Containers

Containers having the configuration illustrated in FIG. 7 were prepared by mounting the check valves of Examples 1-5 and Comparative Example 1 each into an outer body and welding the outer body and the container main body to each other. A multilayer film of PET/ON/L-LDPE was used for a flexible film that constitutes the container main body.

Evaluation Test

The containers according to Examples 1-5 and Comparative Example 1 were each filled with 500 ml of soy sauce to prepare test samples and each sample was subjected to the following drop test. After dropping each sample freely from the respective heights shown in Tables 1 and 2, the occurrence of the mixing of air into the container (air mixing) and the pouring of the soy sauce were evaluated. The occurrence of the mixing of air was determined visually and whether the pouring of the soy sauce was good or not was determined according to whether the soy sauce came out smoothly when the container was 45 degrees inclined. The results are shown in Tables 1 and 2.

TABLE 1 Item Unit Example 1 Example 2 Example 3 Check Outer Diameter of mm 6.41 4.42 4.49 Valve Lid (R₁) Dimensions Inner Diameter of 6.30 4.31 4.30 Main Body (R₂) Difference (R₁ − R₂) 0.11 0.11 0.19 Height of Drop Unit Air Mixing Pouring Air Mixing Pouring Air Mixing Pouring Drop Test 10 cm No Good No Good No Good 20 No Good No Good No Good 40 No Good No Good No Good 60 No Good No Good No Good 80 No Good No Good No Good 100 No Good No Good No Good 120 No Good No Good No Good 140 No Good Yes Not Good No Good 160 Yes Not Good No Good 180 No Good 200 Yes Not Good Note Tow-Mold Type

TABLE 2 Item Unit Example 4 Example 5 Comparative Example 1 Check Outer Diameter of mm 6.35 6.37 6.30 Valve Lid (R1) Dimensions Inner Diameter of 6.29 6.29 6.30 Main Body (R2) Difference (R1 − R2) 0.06 0.08 0.00 Height of Drop Unit Air Mixing Pouring Air Mixing Pouring Air Mixing Pouring Drop Test 10 cm No Good No Good Yes Not Good 20 Yes Not Good No Good 40 Yes Not Good 60 80 100 120 140 160 180 200 Note Nine-Mold Type One-Mold Type

Next, several containers according to Example 1 were prepared and each filled with 500 ml of soy sauce to prepare test samples. The following test was performed for each sample to evaluate the performance of the check valve in more detail.

Static Standing Test

The containers containing soy sauce therein were kept at room temperature and the occurrence of the mixing of air into the container and the pouring of the soy sauce were observed after the elapse of 12, 24, 36, 48 and 120 hours, respectively. Five samples were tested under the respective conditions. The results are shown in Table 3.

TABLE 3 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Conditions Air Air Air Air Air Item Time h Mixing Pouring Mixing Pouring Mixing Pouring Mixing Pouring Mixing Pouring Sealing Test 12 No Good No Good No Good No Good No Good 24 No Good No Good No Good No Good No Good 36 No Good No Good No Good No Good No Good 48 No Good No Good No Good No Good No Good 120 No Not No Not No Not No Not No Not Good Good Good Good Good

After the elapse of 12, 24, 36 and 48 hours, respectively, air mixing did not occur in any samples and the pouring was good. After the elapse of 120 hours (5 days), although air mixing was not observed, some soy sauce hardened at a contact portion (seal portion) between the lid and the peripheral edge of the opening of the main body and the soy sauce did not come out by itself even if the container was inclined.

Drop Test I

The containers containing soy sauce therein were dropped under the respective conditions of (i) and (ii) below. By changing the height from which the container was dropped, the occurrence of the mixing of air into the container and the pouring of the soy sauce were observed after each drop. The evaluation criteria for the occurrence of air mixing and the pouring of the soy sauce were as described above. Five samples were tested under the respective conditions.

(i) No cap was attached to the cap attachment part of the outer body and the container was freely dropped once with the bottom of the container main body down. The results are shown in Table 4.

(ii) A cap was attached to the cap attachment part of the outer body and the container was dropped freely once with the bottom of the container main body down. After that, the container was freely dropped once with the side surface of the container main body down. The results are shown in Table 5.

TABLE 4 Conditions Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Height of Drop Air Air Air Air Air Item cm Mixing Pouring Mixing Pouring Mixing Pouring Mixing Pouring Mixing Pouring Drop Test 80 No Good No Good No Good No Good No Good 120 No Good No Good No Good No Good No Good 140 No Good No Good No Good No Good No Good 160 Yes Not Good Yes Not Good Yes Not Good Yes Not Good Yes Not Good

TABLE 5 Conditions Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Height of Drop Air Air Air Air Air Item cm Mixing Pouring Mixing Pouring Mixing Pouring Mixing Pouring Mixing Pouring Drop Test 80 No Good No Good No Good No Good No Good 120 No Good No Good No Good No Good No Good 140 No Good No Good No Good No Good No Good 160 Yes Not Good Yes Not Good Yes Not Good Yes Not Good Yes Not Good

Regardless of whether a cap was attached or not, air mixing did not occur in any samples until the height of drop reached 140 cm. In addition, the pouring was good. Meanwhile, when the height of drop was 160 cm, the lid of the check valve got stuck and air mixing occurred. In addition, due to the stuck lid of the check valve, the soy sauce did not come out by itself even if the container was inclined. Note that no leakage of the content was observed in any test with a height of drop up to 160 cm.

Drop Test II

Using the container with no cap attached to the cap attachment part of the outer body, the container was freely dropped five times or ten times from a fixed height of drop of 120 cm, with the bottom of the container main body down. The results are shown in Table 6. Two samples were tested under the respective conditions.

TABLE 6 Sample 1 Sample 2 Air Air Item Conditions Mixing Pouring Mixing Pouring Drop Test Consecutive 5 No Good No Good drops of 120 cm Consecutive 10 Yes Not Good Yes Not Good drops of 120 cm

After the consecutive five drops, air mixing did not occur in any samples. In addition, the pouring was good. On the other hand, after the consecutive ten drops, the lid of the check valve got stuck and air mixing occurred. In addition, due to the stuck lid of the check valve, the soy sauce did not come out by itself even if the container was inclined.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 . . . Main body; 1 a, 1 b . . . Opening; 3, 13 . . . Lid; 3 a,         13 a . . . Projection; 3 b, 13 b . . . Side surface; 5 . . .         Hinge; 10 . . . Check valve; 11 . . . Small diameter part; 12 .         . . Large diameter part; 30 . . . Flexible vacuum container         (container); 31 . . . Container main body; 32 . . . Outer body         (spout); 32 b . . . Liquid outlet; F . . . Force; L . . . Linear         portion; P . . . Negative pressure; and R Arc-shaped portion. 

1. A check valve formed of rubber material and manufactured by integral molding, comprising: a tubular main body having openings at opposite ends; a lid arranged to close one opening of the main body; and a hinge that connects the main body and the lid and is adapted to open the one opening when force is applied to the lid outwardly from the main body side, wherein the lid has a projection on a side surface thereof, the projection coming in contact with a peripheral edge of the one opening of the main body.
 2. The check valve according to claim 1, wherein the one opening is constituted by a linear portion which serves as the hinge and an arc-shaped portion.
 3. The check valve according to claim 2, wherein an outer diameter R₁ of an arc-shaped portion of the lid is greater than a diameter R₂ of the arc-shaped portion of the opening and wherein the difference between R₁ and R₂ is from 0.06 mm to 0.50 mm.
 4. The check valve according to claim 3, wherein the side surface of the lid and an inner surface of the main body form an angle of 15-25 degrees.
 5. The check valve according to claim 4, wherein the rubber material has a hardness of 30-80 degrees and an elongation of 200-900%.
 6. A container comprising: a container main body formed of a film; and a check valve according to claim 1, which is attached to the container main body.
 7. The container according to claim 6, further comprising a spout in which the check valve is mounted.
 8. The container according to claim 7, wherein a liquid outlet at a tip of the spout is shaped to be narrowed in the middle and again broadened.
 9. The container according to claim 8, wherein at least part of the main body of the check valve is formed to be thin enough to be able to deform according to a difference from atmospheric pressure when the check valve has a negative pressure inside and thereby allow the check valve to have a reduced volume.
 10. The container according to claim 9, wherein the main body of the check valve has a stepped form composed of a small diameter part and a large diameter part and the one opening is formed at the small diameter part.
 11. The container according to claim 10, wherein the small diameter part is formed to be thinner than the large diameter part.
 12. A method for manufacturing a check valve which comprises: a tubular main body having openings at opposite ends; a lid arranged to close one opening of the main body; and a hinge that connects the main body and the lid and is adapted to open the one opening when force is applied to the lid outwardly from the main body side, the lid having a projection on a side surface thereof, the projection coming in contact with a peripheral edge of the one opening of the main body, the method comprising: a molding step of obtaining a molded body of rubber material in a cavity having a concave portion to form the projection, the rubber material having a hardness of 30-80 degrees and an elongation of 200-900%; a mold-releasing step of removing the molded body from the cavity; and a cutting step of separating the main body and the lid from each other except a portion serving as the hinge. 